The invention relates to an injector for an injection system of an internal combustion engine.
Conventional injectors for injecting fuel into internal combustion engines are generally constructed in a modular manner and consist of a plurality of parts, such as an injector body and a control module which are arranged one above the other with the mechanical connection of two axially adjacent parts being made by means of a connecting element, such as a clamping sleeve, a double clamping nut or a welded sleeve.
The injector is normally fastened in the cylinder head of the internal combustion engine which presses the injector axially into a corresponding receiving bore in the cylinder head. The clamping claw resting on a cylindrical collar which is integrally formed peripherally on the outside of the injector. To prevent the injector from being rotated about its longitudinal axis, key surfaces, which the clamping claw engages, are integrally formed on the outer surface of the injector.
In prior art injectors the cylindrical collar and the key surfaces are fastened either directly to the injector head or to a hollow-cylindrical union nut which receives the individual parts of the injector and is connected on its top side to the injector head. One disadvantage of these injectors is the multiplicity of parts which makes the manufacture and assembly of the injector relatively complicated.
Accordingly, an object of the present invention is to provide an injector for an injection system of an internal combustion engine, wherein the manufacture and assembly of the injector is simplified.
One aspect of the present invention is the utilization of an injector housing which is formed essentially in one piece and which merges at the top into the injector head. The housing is designed to receive at least the control unit. Preferably, the injector housing receives a plurality of injector modules and braces these modules axially relative to one another, in order to effect a high-pressure seal at the joints between adjacent modules.
By using a common housing for the essential components of the injector, separate connection means, such as clamping sleeves, double clamping nuts or welded sleeves, for connecting the individual parts may be dispensed with since the individual parts of the injector are already mechanically fixed by means of the common housing. Furthermore, use of the common injector housing reduces the number of high-pressure sealing surfaces which could result in leaks to the outside.
In accordance with the present invention, it is not necessary for the injector housing to receive all components of the injector and connect them to one another. For example, it is possible for the nozzle body on the underside of the injector to be attached to the injector housing via a conventional clamping nut, while the remaining components of the injector, such as the control unit, are located in the injector housing.
Another aspect of the present invention contemplates omitting a separate transmission lever for transmitting the actuating movement of the actuator to the valve piston, with the actuator acting directly on the valve piston. By doing away with one component of the injector, the outlay in terms of manufacture and assembly is further reduced. Furthermore, by dispensing with a conventional transmission lever, the durability of the injector is increased, since the useful life of such a transmission lever is problematic.
Due to a reduced surface pressure, the bearing surface between the actuator and the valve piston has a liquid film between the actuator and the valve piston, even during a switching operation, and thus effects an hydraulic play compensation. The mutually confronting end faces of the actuator and/or the valve piston are preferably convexly shaped, in order to prevent the liquid film from breaking away under mechanical load during a switching operation. However, the end faces may also be completely planar, thus allowing simple length adjustment by measurement and grinding down.
A spring is preferably arranged between the actuator and the valve piston which presses the actuator and the valve piston apart in the axial direction. This feature also provides full play compensation when the injector is in the rest state. Such a spring advantageously enables thermal expansions to be compensated for.
In a further variation of the present invention, the valve piston of the injector is not guided directly in the injector housing, but is mounted in a separate valve housing which is arranged within the injector housing. This affords the advantage that the valve seat of the valve piston is located in a valve housing, not in the injector housing. This eliminates the need for any complicated heat treatment of the entire injector housing.
In another aspect of the present invention, a continuous leakage line is omitted and the central bore for the control members is used for leakage return from the nozzle to the control unit. The leakage line is connected to the central bore preferably by means of a radial connecting bore. Above the control unit, leakage is carried via a separate line. This aspect of the present invention further improves injector manufacturing efficiencies.
The injector according to the present invention is preferably used in a common-rail injection system, although the invention is not restricted to that use, and, in principle, may be used in other types of injection systems.